1. Field of the Invention
This invention relates generally to electrical shift-by-wire selection of a desired transmission operating range, and more particularly to a method for testing operation of the park failsafe portion of a shift-by-wire system.
2. Description of the Prior Art
In a conventional automatic transmission system for a motor vehicle, a direct mechanical linkage connects the driver operated gear shift lever, whose movement actuates the transmission gear shift mechanism through a cable.
In a shift-by-wire system this direct linkage is separated from the driver, and an electronic system that includes solenoids or motors may be used to produce the intended position of the gear shift mechanism. In such an electronic system, redundant systems are sometimes applied to ensure functionality under unexpected conditions. These systems would typically apply some form of secondary mechanical or hydraulic system that operates upon the failure of the primary function of the system.
A key challenge is to provide proper verification of the secondary system to ensure its functionality before using the system under a condition where the function is absolutely necessary.
In the case of a system that uses stored mechanical energy, operation of the secondary system can be difficult due to the difference in audible characteristics and response time differences. The nature of this response could raise user concerns that something abnormal occurred.
A need exists for an improved method that verifies the system without creating new problems by testing a backup system. The method should ensure that, during verification testing, the actuator assembly remains in the intended gear level position without unintentionally producing an unintended gear position.
The specific mechanism being considered for this proposal is an electro-mechanical backup system which uses a torsion spring of sufficient capacity that can return the system back to a gearshift park state independent of the primary functional system.